Chemistry (English) - For Class SSC - Part 1 (Science Group) - Solved Model papers 2020 -2021- AS PER CONDENSED SYLLABUS

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Chemistry (English)
For Class SSC - Part 1 (Science Groups)
Solved Model papers 2020 - 2021
As Per condensed Syllabus

Special Thanks To Sir Waseem Ahmed Qureshi
BS Zoology (UOK)
# 0315 - 0226373

Note: The correct answer of XXI is Molecular Mass

SECTION "B" (SHORT ANSWERS QUESTIONS) (18 Marks)

Note: Answer any six (6) questions from this section. Each carries 3 marks.

Q.2: What is meant by Mole? Calculate the number of moles in 96g of SO₂.
Ans: Mole:
The molecular mass, atomic mass and formula mass of a substance expressed in grams is called mole.

Data:
No. of Mass = ?
Given Mass = 96 g
Molecular Mass Of SO₂ = ( 32 + 16 x 2) = 32 + 32 = 64 a.m.u

Solution:
We know that:
Mole = ^{Given Mass of a substance}/_{Atomic mass OR Molecular mass}
= ⁹⁶/₆₄
= ³/₂
= 1.5 moles Ans

Q.3: Write down any three chemical properties of acids.
Ans: CHEMICAL PROPERTIES OF ACIDS:
"Acid react with bases, metals, non-metals and other things etc. Some of the properties are given below."

1. Neutralization:
"Acids react with bases to form salt and water, this is called Neutralization."

HCl + NaOH → NaCl↓ + H₂O

Hydrochloric acid + Sodium hydroxide → Sodium chloride (salt) + Water

2. Reaction with metals:
"Dilute acid reacts with certain metals such as (Zn, Mg and Fe to produce H₂ gas)"
For example: Dilute Hydrochloric acid reacts with Zn metal to produce H₂ gas.

Zn + 2HCl_(dil) → ZnCl↓₂ + H₂↑

Zinc + Hydrochloric acid (dilute) → Zinc chloride (salt) + Hydrogen gas

3. Reaction with carbonate and bicarbonates:
Acid react with carbonate and bicarbonate salts to produce CO₂ gas.

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂

Sodium carbonate + Hydrochloric acid → Sodium chloride + Carbon dioxide

4. Reaction with oxides and hydroxides of metals:
Metal oxide and hydroxide react with acid to form salt and water like neutralization.

FeO + H₂SO₄ → FeSO₄ + H₂O

Ferrous oxide + Sulphuric acid → Ferrous sulphate + water

(Note: Do any three properties as mentioned in question)

Q.4. Define Ionic bond. Describe the mechanism of formation of NaCl.
Ans: IONIC BOND:
The electrostatic force of attraction between oppositely charged ions is called ionic bond or electrovalent bond.

Example #1:
Formation Of Ionic Bond In Sodium Chloride (NaC1):
The combination of sodium (Na) and chlorine (Cl) atom to form common salt. sodium chloride (NaC1), An atom of sodium (Na) transfers one electron and become positive sodium ions (Na⁺) and an atom of chlorine gains that electron to complete octet and becomes chloride negative ions (Cl^-)

Na → Na⁺ + e^-
2,8,1 → 2,8 + 1 (electronic configuration)

Cl + e^- → C1^-
2,8,7 + 1 → — 2,8,8 (electronic configuration)

Na⁺ + Cl^- → NaC1

The oppositely charged Na⁺ and Cl⁺ are held together By electrostatic force of attraction and ionic bond produced between them.

Example #2:
Formation Of Ionic Bond In Magnesium Oxide:
Magnesium (Mg) has two electrons in its valance shell while Oxygen has six electrons in its valence shell. Magnesium atom losses two electrons and become magnesium ion (Mg⁺²) and Oxygen (0) gains two electrons and becomes oxygen ion (O^-2). thus attain a stable noble gas structure by having eight 8 electrons in their valence shell. Mg⁺² and O^-2 attracts each other to form Mg⁺²O^-2.

Mg → Mg⁺² + 2e^-
2,8,2 → 2,8 + 2 (electronic configuration)

O + 2e^- → O^-2
2,6 + 2 → — 2,8

Mg⁺² + O^-2 → MgO

Q.5: Balance the following Chemical equations by using co-efficient:
i) N₂ + H₂ → NH3 (Hint: Balance hydrogen on R.H.S first)

N2 + H2 → NH3
N = 2	N = 1 x 2 = 2
H = 2 x 3 = 6	H = 3 x 2 = 6
N2 + 6H2 → 2NH3 (Balanced)

ii) CH₄+ O₂ → CO₂ + H₂O (Hint: Balance hydrogen on R.H.S first)

CH4+ O2 → CO2 + H2O
C = 1	C = 1
O = 2 x 2 = 4	O = 2 + 1 = 3 = 2 + 1 x 2 = 2 + 2 = 4
H = 4	H = 2 x 2 = 4
CH4+ 2O2 → CO2 + 2H2O (Balanced)

iii) KNO₃ → KNO₂ + O₂  (Hint: Balance Oxygen on L.H.S first)

KNO3 → KNO2 + O2
K = 1 x 2 = 2	K = 1 x 2 = 2
N = 1 x 2 = 2	N = 1 x 2 = 2
O =  3 x 2 = 6	O = 2 + 2 = 4 = 2 x 2 + 2 = 4 + 2 = 6
2KNO3 → 2KNO2 + O2 (Balanced)

Q.6: Find out Protons and Neutrons present in the following atoms

1. ₇N¹⁴
2. ₁₇Cl³⁷
3. ₉₂U²³⁵

i) Nitrogen ₇N¹⁴
Data:
Mass number Or Atomic mass = A = 14
Atomic number = Number of electrons = Z = 7
Proton or P⁺ = ?
Neutron no. = N = ?

Solution:
We know that Proton number is equal to electrons or Atomic number So,
Proton (P⁺) = Z = 7

We also know that
Mass number = No. of Proton + No. of Neutron
A = P⁺ + N or
N = A - P
= 14 - 7 = 7

Ans:
Number of Proton = 7
Number of Neutron = 7

i) Chlorine ₁₇Cl³⁷
Data:
Mass number Or Atomic mass = A = 37
Atomic number = Number of electrons = Z = 17
Proton or P⁺ = ?
Neutron no. = N = ?

Solution:
We know that Proton number is equal to electrons or Atomic number So,
Proton (P⁺) = Z = 17

We also know that
Mass number = No. of Proton + No. of Neutron
A = P⁺ + N or
N = A - P
= 37 - 17 = 20

Ans:
Number of Proton = 17
Number of Neutron = 20

i) Uranium ₉₂U²³⁵
Data:
Mass number Or Atomic mass = A = 235
Atomic number = Number of electrons = Z = 92
Proton or P⁺ = ?
Neutron no. = N = ?

Solution:
We know that Proton number is equal to electrons or Atomic number So,
Proton (P⁺) = Z = 92

We also know that
Mass number = No. of Proton + No. of Neutron
A = P⁺+ N or
N = A - P
= 235 - 92 = 143

Ans:
Number of Proton = 92
Number of Neutron = 143

Q.7: What are Transition Elements? Describe any two general characteristics of these elements?
Ans: TRANSITION ELEMENTS:
Elements in group IB, IIB to VIIB are known as transition elements because they show their variable valency which are transitional between highly reactive and strong positive elements of S-Block elements which form ionic compounds and P-Block which form largely covalent compounds.

Characteristics:

1. Transition elements have incomplete inner electron shells and are characterized by their varaiable valencies and show similar behaviors.
2. All transition elements are metals, in which bonds between the atoms are very strong.
3. They have high melting point.
4. The compounds are formed by coordinate covalent bonds.

(Note: Write down any two characteristics as mentioned in question)

8. Define both kinds of Displacement reaction with an appropriate chemical equation as example for each.
Ans:
1) SINGLE DISPLACEMENT REACTION: (2006, 2007, 2008)
A reaction in which one atom or groups of atoms of a compound replaced by another atom or group of atom in a compound is called single displacement reaction.

Example:

Fe + CuO → FeO + Cu

Cu + HSO₄ → CuSO₄ + H₂

2) DOUBLE DISPLACEMENT REACTION: (2013)
A reaction in which two compounds exchange their partners, so that two new compounds are formed is called double displacement reaction. Insoluble salts are formed by mixing soluble salts.
Example:

AgNO₃ + NaCl → AgCl + NaNO₃

AgNO₃ + HCl → AgCl + HNO₃.

Q.9: What is diffusion? State Graham's law of diffusion of gases.
Ans: DIFFUSION: (2007, 2008, 2010, 2013, 2012, 2014, 2016, 2019)
The spreading of substance from higher concentration level to lower concentration level is called diffusion.

GRAHAM'S LAW OF DIFFUSION:(2005,2009,2010,2015,2019)
Thomas Graham in 1864 studied the rate of diffusion of different gases and formulated Graham's law.
Statement:
The rate of diffusion of gas at a constant temperature and pressure is inversely proportional to the square root of its density or Molar mass.

Mathematically:

Q.10.:Calculate the molarity of a solution that contains 2 moles of NaOH dissolved in 0.5 liter of the solution.
Data:
No. of moles = 2 moles
Volume of solution = 0.5 liter
Molarity = ?

Solution
We know that;

Molarity = ^{Moles of solute}/_{Volume of solu. (liter)}

Molarity = ²/_0.5

Molarity = 4 M Ans.

SECTION- "C" (DESCRIPTIVE ANSWER QUESTIONS)

Note: Answer any two (2) questions from this section. Each carries 6 marks.
Q.11: Define Solubility then list the factors affecting solubility and elaborate any two of them.
Ans: SOLUBILITY: (2008, 2009, 2015, 2016)
The amount of solute dissolved at a room temperature in 100 gm of the solvent is called solubility.

Factors Affecting the Solubility: (2008)
Many factors are affecting the solubility of a solute in a solvent, these factors may be:

1. Temperature
2. Pressure (for gasses)
3. Nature of solute and solvent

1) Temperature: (2008,2016)
The solubility of many solutes generally increase with the increase in temperature such solute absorb heat when they dissolved in water.
Example: solubility of sugar in water at 0 °C is 179 g / 100 ml where as at 100 °C it is 487 g / 100.

2) Pressure: (2016)
Solubility of Solids and Liquids:
The solubility of solid and liquid are not affected by pressure.
Henry's Law:
Solubility of a Gas of gas in a liquid:

"The solubility of gas in liquids is directly proportional to the pressure of gas."

This is called Henry's law.

m ∝ P

m = KP

where,
m = amount of gas
K = constant and
P = pressure

Example: This effect is used in manufacture of bottled soft-drinks as coca-cola; 7-up etc. these are bottled under a carbon dioxide (CO₂) pressure slightly greater than 1 atm. When the bottles are opened, pressure decreases, solubility of CO₂ also decreases, hence bubbles of CO₂ comes out of solution.

3) Nature of solute and solvent:
Solubility:
If a solute is also depends upon nature of the solute and the solvent. Polar compound is more soluble in polar solvent than non-polar solvent. Similarly covalent compounds are more soluble in non-polar solvent.
Example: Napthalene being a non-polar solute is more soluble in benzene (non-polar solvent).

Q.12: State Faraday's law of Electrolysis and explain any one of them.
Ans: FARADAYS LAW OF ELECTROLYSIS:
Introduction: Michael Faraday in 1833, discovered laws of electrolysis which are known as Faraday's law of electrolysis put forward by Faraday.

FIRST LAW OF FARADAY:

"The amount of any substance deposited or liberated at an electrode during electrolysis is directly proportional to the quantity of electricity passed through electrolyte."

Explanation: Faraday's law expressed mathematically.

W ∝ A X t

W = Z x A x t

Where,
A = Current in amperes
Z = Electrochemical equivalent of substance.
T = Time in seconds.
W = mass of substance

The quantity of substance deposited by one faraday (96,500 coulombs) of electricity through an electrolyte is called one Gram chemical equivalent of that substance.

SECOND LAW OF FARADAY:

"When the same quantity of electricity is passed for the same time through different electrolytes connected in series, the substances deposited at the electrode will be in the proportional to their equivalent masses."

13. What is Salt? On the basis of chemical properties describe its three kinds with example.
Ans: SALT:
A salt is ionic compound produced when acid is neutralized by a base.
For example:
Potassium hydroxide neutralized hydrochloric acid to form potassium chloride (salt) and water.

KOH + HCl → KCl + H₂O

Types of Salts:
On the basis of their chemical nature salts can be divided into three groups which are:

1. Normal salt
2. Acidic salt
3. Basic salt

1. Normal Salts:
Salts which are formed by the complete neutralization of an acid by a base. These salts do not have replaceable hydrogen ions (H⁺ or hydroxyl ion (OH^-).
Example: NaC1, NaNO₃, K₂SO₄ etc. are normal salts.

HCl + H₂O → NaCl + H₂O

2. Acidic Salts:
Salts which are formed by the partial or incomplete neutralization of an acid by a base. These salts have replaceable hydrogen ions (H⁺. They react further with base to form normal salts.
Example: KHSO₄, NaHCO₃, NaHSO₄, KHCO₃etc are acidic salts.

KOH + H₂SO₂ → KHSO₂ + H₂O

NaOH + H₂CO₃ → NaHCO₃ + H₂O

3. Basic Salts:
Salts, which are formed by the partial or incomplete neutralization of a base by an acid. These salts have replaceable hydroxyl ions (OH^-.
Example: Mg (OH)Cl, Zn (OH) Cl etc. are basic salts.

Q.14: Write down any four differences between covalent bond and co-ordinate covalent bond.
Ans: Differences Between Covalent Bond And Co-ordinate Covalent Bond.

S.NO.	COVALENT BOND	CO-ORDINATE COVALENT BOND
1.	A covalent bond forms by mutual sharing of electrons from both atoms.	A co-ordinate covalent bond forms by one sided sharing of electrons.
2.	The covalent bond is formed between the similar or dissimilar atoms.	Co-ordinate covalent bond is formed between two unlike or dissimilar ateats.
3.	Covalent bond maybe polar or non-polar.	Co-ordinate covalent bond is always polar.
4.	Covalent bond is associated with only covalent character.	Co-ordinate covalent bond is associated with ionic and covalent character,

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